(a) Technical Field
The present disclosure relates, generally, to an electrolyte membrane for a fuel cell. More particularly, it relates to a novel amphiphilic block copolymer, a method for manufacturing the same, and a polymer electrolyte membrane using the same.
(b) Background Art
As an electrolyte membrane for a polymer electrolyte membrane fuel cell (PEMFC), fluorine electrolyte membranes are typically used. Although the fluorine electrolyte membranes have high chemical and mechanical stability and show excellent ion conductivity, the manufacturing cost is high due to a complicated manufacturing process and they show significant performance deterioration at a temperature of more than 80° C. Accordingly, hydrocarbon electrolyte membranes such as PAES, sPEEK, sPPBP, PI, etc. have been reported. However, a large amount of hydrophilic groups are required to improve the ion conductivity, which can cause a problem in the dimensional stability due to high moisture-containing properties of the membrane. The low dimensional stability has a bad effect on the manufacturing process of a membrane-electrode assembly (MEA) and its long-term stability. As a result, block copolymer polymer electrolyte membranes have been proposed. Block copolymers exhibit high ion conductivity and excellent dimensional stability even at low moisture content.
Nafion membranes (Dupont) are most commonly used as proton exchange membranes (PEMs) and have high hydrogen ion conductivity and excellent chemical stability. It is known that such a high hydrogen ion conductivity results from the microphase separation of hydrophilic and hydrophobic groups. However, the manufacturing cost is high and they show significant performance deterioration at a temperature of more than 80° C. Especially, in the case where the polymer electrolyte membrane fuel cell is operated at a high temperature of more than 100° C., (1) the resistance of platinum catalyst to impurities is increased, (2) the reaction rate at oxidation and reduction electrodes is increased, (3) the management of water in the fuel cell is easy, and (4) the cooling system is simplified. Accordingly, there is an urgent need in the art to develop a high-temperature polymer electrolyte membrane fuel cell (PEMFC). To this end, extensive research on sulfonated poly(ether ether ketone), sulfonated poly(arylene ether sulfone), etc. using engineering plastics having excellent thermal and mechanical stability has continued to progress to develop an electrolyte membrane which can be operated at high temperatures. However, in cases where these engineering plastics are used, the microphase separation between the hydrophilic and hydrophobic components, which is required to form ion channels, is not satisfactory.
Therefore, the inventors of the present invention have tried to develop an alternative electrolyte membrane which can solve the above-described problems and, as a result, have developed a novel amphiphilic block copolymer, and an electrolyte membrane for a fuel cell including the same.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.